According to the protein-only hypothesis, infectious prions are composed exclusively of a misfolded glycoprotein, PrPSc, which is formed by conformational change of a chemically indistinguishable host protein, PrPC. Prions can exist in multiple, self- replicating strains, characterized by unique clinical, pathological, and biochemical features. A phenomenon not easily explained by the protein-only hypothesis is selective neurotropism, in which the pattern of PrPSc accumulation in different brain regions is determined by the prion strain. The mechanism(s) by which cells recognize and distinguish between different prion strains remains unknown. In this competitive renewal application, we propose three specific aims to determine the molecular basis of prion neurotropism. 1. Test the hypothesis that PrPSc glycosylation controls the neurotropism of prion strains. 2. Test the hypothesis that accessory polyanions control the neurotropism of prion strains. 3. Compare the composition of prion deposits associated with different strains. PUBLIC HEALTH RELEVANCE: Transmissible Spongiform Encephalopathies (TSEs), also known as prion diseases, are a unique group of slowly progressive and invariably fatal infections of the central nervous system, which can occur in infectious, sporadic, and inherited forms. Some examples of TSEs include kuru and Creutzfeldt-Jakob disease (CJD) in humans, bovine spongiform encephalopathy (BSE) in cattle, chronic wasting disease (CWD) in deer and elk, transmissible mink encephalopathy (TME) in mink, and scrapie in sheep. The infectious agents of TSEs are unconventional, proteinaceous entities, which have been termed prions. In this application, we propose to study the mechanisms responsible for prion dissemination through the brain. These studies may eventually lead to improved methods to diagnose and treat prion TSEs, and may also provide insights into the pathophysiology of related neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases.